The present invention relates to a method for the separation of useful substances from soaps, such as pulping soap obtained as a by-product in the production of sulfate cellulose or soaps obtained from deodorized distillates of plant oils. More precisely the invention relates to a method for extracting unsaponifiable neutral substances from different kind of soaps. The invention also relates to a method for extracting, separating and purifying sterols from soaps.
Soaps contain a lot of alkali salts of fatty and/or resin acids and variable amounts of unsaponifiable neutral substances consisting of e.g. phytosterols, terpene alcohols, fatty alcohols, and aldehydes, ethers, ketones as well as hydrocarbons. Small amounts of fibres, lignins and inorganic salts also exist as impurities in the soap. The amount of neutral substances varies depending on the wood material used for pulping.
Tall oil, made from soaps by acidulation is a valuable raw material for the chemical industry, but generally the neutral substances included in it are not utilized at all. However, from the neutral substances many valuable raw materials can be isolated, such as phytosterols, which can be used e.g. in the food, pharmaceutical and cosmetic industry. Because of the many beneficial characteristics of the phytosterols, the need thereof has grown enormously during the last years. Besides producing hormone preparations by steroid transformations they are used in foodstuffs or medical preparations especially for lowering serum total and LDL cholesterol levels. Most preferable for this kind of use are the stanols and especially the stanol esters, which can be produced e.g. by hydrogenation and esterification of phytosterols.
One method for extracting neutral substances from soaps was proposed in U.S. Pat. No. 2,866,781. In the method proposed therein, esters of a relatively low molecular weight aliphatic acid are used as extraction solvents for aqueous soap solutions. These extraction solvents are, however, not very selective for the neutral substances.
U.S. Pat. No. 3,965,085 discloses a method for refining soaps in which the unsaponifiable neutral substances included in the soap are separated by means of extraction from an aqueous solution containing low molecular weight ketones, such as acetone or methyl ethyl ketone, using as the water-immiscible solvent an aliphatic, aromatic, alicyclic or halogenated hydrocarbon. In the Examples of this patent, extraction is conducted at temperatures below 75xc2x0 C. The added ketone is essential in the disclosed extraction method, since it prevents the formation of emulsions in the soap solution and thereby facilitates the extraction process.
U.S. Pat. No. 2,530,809 discloses the extraction of neutral substances from tall oil soaps using a mixture of the soaps with a lower alcohol and water. Suggested as solvents for the unsaponifiable material are alkanes or other petroleum fractions, ethers, aromatic hydrocarbons or chlorinated hydrocarbons. The extraction procedure is conducted at temperatures of between 80 and 120xc2x0 F. (which is between about 27 and 49xc2x0 C.). In this case, the lower alcohol acts as an emulsion breaker.
Problems with the two extraction methods described in U.S. Pat. No. 3,965,085 and U.S. Pat. No. 2,530,809 are particularly focused on their use of a two-component solvent system, which involves difficult solvent regeneration systems in large scale production. Complete removal of the alcohol (U.S. Pat. No. ""809) or the ketone (U.S. Pat. No. ""085) from the soap solution is also technically impossible, because of foaming problems. The remaining solvent is also to some extent harmful for further processing of the soap. If present, it causes problems e.g. in the distillation of crude tall oil. But, above all, the inevitable solvent losses in these methods make them not very economic and these methods do not take into account environmental aspects.
FI 55 679 discloses an extraction method wherein a long chain C12-C35 hydrocarbon in combination with water is used for extracting neutral substances from soap. This method suffers from the drawbacks involved in using long chain hydrocarbons, which need very high temperatures for regeneration and therefore are not particularly suitable in large scale production. Another problem involved with this method is that the long chain hydrocarbons and the light fractions of the neutral substances have boiling points close to each other, and the recirculation of this solvent may therefore lead to higher amounts of light fractions of the neutral substances in the process system.
All the prior disclosed methods for extracting neutral substances from soaps have some technical problems, which have been solved by the methods according to the present invention.
It has now surprisingly been realized that neutral substances can be extracted from different kind of soaps by the use of a short chain (C1-C10) hydrocarbon solvent and an aqueous solution of the soaps. This allows the best regeneration system for the solvent, and the problems associated with the use of long chain hydrocarbons are avoided. No other organic solvent is needed in the method of the invention because, instead of using additives such as alcohols or ketones as in the art, emulsion breaking can be accomplished by increasing the temperature of the mixture to at least 140xc2x0 C., and thereby the phase separation needed for the extraction to proceed is accomplished.
In a first aspect of the present invention there is provided a method for the separation of neutral substances from soaps comprising the steps of:
extracting neutral substances into a hydrocarbon phase by mixing the soap with water optionally containing sodium sulfate, and with a short chain hydrocarbon solvent at ambient or elevated temperature, and raising the temperature of the mixture to at least 140xc2x0 C., to obtain a hydrocarbon phase containing neutral substances, and a soap phase, the extraction step being conducted in a closed system, wherein the pressure in the system is at least equal to the vapor pressure of the extraction mixture at the temperature used for extraction,
separating the hydrocarbon phase containing neutral substances from the soap phase, and
optionally separating the neutral substances from the hydrocarbon phase.
In a second aspect of the present invention there is provided a method for the separation of sterols from soaps comprising the steps of:
extracting neutral substances into a hydrocarbon phase by mixing the soap with water optionally containing sodium sulfate, and with a short chain (C1-C10) hydrocarbon solvent at ambient or elevated temperature, and raising the temperature of the mixture to at least 140xc2x0 C., to obtain a hydrocarbon phase containing neutral substances, and a soap phase, the extraction step being conducted in a closed system, wherein the pressure in the system is at least equal to the vapor pressure of the extraction mixture at the temperature used for extraction,
separating the hydrocarbon phase containing neutral substances from the soap phase,
optionally separating the neutral substances from the hydrocarbon phase,
separating sterols from the hydrocarbon phase containing neutral substances or from the neutral substances, and
optionally purifying the sterols.
The above steps (a) to (c) can be carried out as explained above for the first aspect of the present invention.